# CVE-2026-45056: Matrix Rust SDK: Sender-binding gaps in to-device and room-key attribution

> Attackers colluding with homeservers can forge encrypted to-device events by bypassing sender identity checks in the Matrix Rust SDK.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 14 Sep 2026
- **Also known as:** GHSA-wfq4-36m3-9g42, RUSTSEC-2026-0159

## What is CVE-2026-45056?

CVE-2026-45056 is a medium-severity authentication bypass vulnerability in matrix-org matrix-rust-sdk, published on 11 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

matrix-sdk-crypto is a no-network-IO implementation of a state machine that handles end-to-end encryption for Matrix clients. Starting in version 0.12.0 and prior to version 0.17.0, the matrix-sdk-crypto crate was missing a check for the user ID when decrypting an Olm-encrypted event containing the `sender_device_keys` property. This could be exploited to forge an encrypted to-device event, but only if the attacker colludes with the homeserver operator. This issue is fixed in matrix-sdk-crypto 0.17.0. There are no known workarounds for the issue.

Weakness: CWE-290 (Authentication Bypass by Spoofing)

## Which versions are affected by CVE-2026-45056?

3 open source packages ship an affected version, including matrix-sdk-crypto.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `matrix-sdk-crypto` | crates.io | From 0.12.0 | 0.16.1 |
| `matrix-sdk-crypto` | crates.io | From 0.12.0 | 0.16.1 |
| `matrix-sdk-crypto` | crates.io | From 0.12.0 | 0.16.1 |

## How do I fix CVE-2026-45056?

Upgrade matrix-sdk-crypto to 0.16.1 or later.

## Is CVE-2026-45056 being exploited?

There is no known exploitation of CVE-2026-45056 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45056 and fix it if it is affected.

What it is: CVE-2026-45056 is a medium-severity authentication bypass vulnerability in matrix-org matrix-rust-sdk, published on 11 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-45056 in the wild and no public exploit code.

Affected packages and fixed versions:
- matrix-sdk-crypto (crates.io): affected from 0.12.0; fixed in 0.16.1
- matrix-sdk-crypto (crates.io): affected from 0.12.0; fixed in 0.16.1
- matrix-sdk-crypto (crates.io): affected from 0.12.0; fixed in 0.16.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-45056/ (Markdown: https://insights.sbomify.com/CVE-2026-45056/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45056
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45056
- OSV: https://osv.dev/vulnerability/CVE-2026-45056

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45056/
Summaries are generated and may contain mistakes; the official description above is the record.